In conventional photographic processing apparatus for processing of photographic material, the material being processed follows a predetermined sequence of steps through the apparatus. For example, when processing a conventional color negative film using the C-41 process, the film follows these processing steps: developer, bleach, first wash, fixer, second wash, and stabilizer.
In conventional processing apparatus, this requires the provision of at least two wash tanks as the film is traditionally processed by following a fixed path through the processor. The use of wash water between processing steps as discussed above is described in GB-A-1 493 170 and DE-A-34 23 671.
Prewashing baths are also known in the art. For example, JP-A-62 38465 discloses the use of a prewash bath between the developing step and the wash step, and JP-A-63 143548 discloses the use of a preliminary wash tank between the fixing step and the wash step.
It is also known in the art to have more than one washing step and the water from a later wash step is recovered for use in an earlier wash step. This is discussed in JP-A-62 38465 mentioned above, and also in GB-A-2 062 265 and EP-A-0 512 321.
However, in the apparatus used to carry out the processes discussed above, more than one wash tank is always provided.
With the advent of minilabs and the need to make processing apparatus smaller, it was found that the first wash step could be removed from the C-41 process for processing of color negative film as discussed above. This made the process quicker and the apparatus shorter as one less wash tank is required.
However, there are several disadvantages associated with the removal of this first wash step:
1) The fixer solution becomes contaminated with bleach. In particular, bromide is carried in from the bleach which makes the fixing step slower. Iron complexes also carried in from the bleach make electrolytic silver recovery processes from the fixing solution using conventional means less efficient.
2) The developer raises the pH of the bleach. In processing of color negative film, the bleaching step is usually acidic and the developing step alkaline. Developer carried over into the bleaching step from the previous step, increases the bleaching time due to the raised pH of the bleach.
3) Dye stains form in the film. This is due to the developer being oxidized in the bleach and reacting with the couplers in all areas of the film which is not imagewise dependent.
4) High levels of pollutants in the effluent from the process. This is because acid is added to the bleach to prevent dye stain formation by neutralization of the coupler anions in the film. The acid usually used is acetic acid which produces high levels of biological oxygen demand (often expressed as BOD.sub.5) in the effluent.